1. Field of the Invention
In general, the invention relates to medical devices and, more specifically, to medical devices for blood vessel access.
2. Description of Related Art
The human vascular system includes three major types of blood vessels: arteries, muscular, relatively high-pressure vessels that carry blood away from the heart and toward the organs and tissues; veins, lower pressure vessels that return blood from the organs and tissues to the heart; and capillaries, the network of small vessels that distribute blood within the organs and tissues and connect the arteries with the veins.
During the course of medical treatment, it is often necessary to access the vascular system, for example, to deliver drugs or treatments, to take blood samples, and to gather information about the patient's vascular pressures and other aspects of their condition. Many procedures require access through a vein; other procedures require access through an artery. Generally, a hollow needle with either a syringe or a catheter attached is inserted into an artery or vein in order to obtain access.
However, it may be difficult for a clinician to determine whether he or she has punctured an artery or a vein. Differentiating between the two can be critical, for several reasons. For one, because arteries are typically at higher pressure than veins, inadvertently puncturing an artery can cause a great deal of bleeding. Aside from the immediate concern of bleeding, delivering a treatment designed for a vein into an artery can have serious adverse consequences for the patient.
Because of the importance of determining whether an artery or a vein has been entered, some techniques have evolved to differentiate between the two. For example, a physician seeking to place a central line in a patient might seek out, for example, the internal jugular vein by using a needle attached to an ordinary syringe. As the needle enters an artery or vein, the syringe fills with blood. Typically, the surgeon then tries to ascertain whether the vessel in question is an artery or vein by observing such things as the color of the blood (bright red oxygenated blood typically indicates an artery), the presence of a strong, pulsatile flow to the blood (also indicative of an artery), and the rate at which the syringe fills with blood (faster filling generally indicates an artery).
However, those observational techniques for differentiating between artery and vein are sometimes unreliable—for example, some patients may have an elevated venous pressure, and other patients, like hypovolemic patients, may have a deceptively low arterial pressure. In order to obtain a more definitive answer, the physician could, for example, disconnect the syringe from the needle and attach a pressure transducer, or could send the blood to a laboratory for a blood gas analysis, among other techniques. However, those techniques take more time, require more equipment, and may not be practical in emergency situations.